Specific aims of this study are 3-fold: 1) to examine any possible inhibitory effects of N-acetylcysteine (NAC) on the growth of S. sanguis D1, S. mitis MT and S. mutans strain 6715 in vitro; 2) to study the effect of NAC on adsorption of salivary glycoproteins on spheroidal hydroxyapatite (SHA); and 3) to study the effect of NAC on attachment of these 3 organisms to SHA and to SHA coated with salivary glycoprotein. The effect of NAC on growth of these oral microorganisms will utilize the serial dilution technique for determining Minimum Inhibitory Concentration. To examine the effect of NAC on salivary glycoprotein adsorption, SHA will be agitated with 1, 2, 5 and 10% NAC for 5 minutes, sedimented and washed with phosphate buffer. Samples of thus treated SHA and non-NAC treated SHA will be agitated with whole unstimulated saliva for 1 hr. Protein concentration of saliva exposed to SHA will be compared to saliva samples that have not been exposed to SHA. Adsorbed glycoproteins will be eluted with 0.2 M phosphate buffer, pH 7, and proteins determined by disc gel electrophoresis. For bacterial adsorption studies, 50 mg samples of SHA, with and without salivary glycoprotein coating, will be exposed to 1, 2, 5 and 10% NAC for 5 minutes, sedimented, washed with phosphate buffer and suspended in culture medium containing similar populations of tritium-labelled organisms for 1 hr. Non-NAC-treated SHA, with and without saliva coating, will be carried through the same procedures as controls. SHA with adsorbed bacteria will be allowed to settle and supernatant removed. The unadsorbed cells contained in 1 ml samples of the supernatant will be collected on 0.45 Mum membrane filters and the filters counted in a scintillation spectrometer. The SHA with adsorbed bacteria will be washed in buffered KCl, transferred to scintillation vials and counted. Known numbers of bacteria in 0.1 ml will be added to 50 mg samples of SHA and counted in a similar manner.